JPH0210277B2 - - Google Patents

Abstract

The disclosure concerns the wire end section of a paper making machine. The wire belt is an endless loop and the pulp suspension is supplied by one or more head boxes. The head box has an upstream and a downstream flow guide wall defining a pulp outlet opening between them. The downstream guide wall has a convexly curved slide shoe which cooperates with the passing wire belt to define a web-forming zone. At the other side of the wire belt, upstream of the outlet opening, another convexly curved wire support surface is defined for leading the wire belt into the web-forming zone. Both of the convexly curved surfaces are displaceable transversely to the direction of pulp flow from the head box. The radius of curvature of the slide shoe is greater at the outlet opening and smaller away from the outlet opening. The radius of curvature of the cooperating supporting surface on the other side of the belt is smaller than the mean radius of curvature of the slide shoe. Where a plurality of head boxes are provided, drainage water from one head box is collected and is pumped to supply water for the other head box, and vice-versa.

Description

DETAILED DESCRIPTION OF THE INVENTION The invention relates to a wire part as indicated in the preamble of claim 1. A device of this kind is known from DE 2908791, ie US Pat. No. 4,308,097. In this case, the wire belt passes through the outer surface of the other flow guide wall of the flow box before passing over the curved extension of the flow guide wall of one of the flow boxes together with the cellulose sheet on which the wire belt is formed. be guided. A disadvantage of this device is therefore that the channel defined by the two flow guide walls has to be turned around relatively sharply in the region of the outlet. That is, in other words: The central streamline of the pulp stream has a smaller radius of curvature in the region of the outlet than in the sheet-forming zone. Thereby, at high operating speeds, there is a risk of the formation of side streams in the sheet-forming zone that - viewed in longitudinal section - extend transversely to the main flow direction. This results in non-uniform fiber distribution. In more extreme cases, cavitation phenomena must be taken into account.

Another drawback is that when the wire belt is associated with multiple back-to-back flow boxes to produce multilayer products, it is necessary to transfer this onto the felt after forming the first fiber sheet layer. That is to say. The wire must then be fed into a second flow box, whereby the fiber sheet layer formed here must be transferred again onto the felt. This is repeated several times if necessary. The flow box then has to be installed in a very narrow space between the wire belt on the one hand and the felt belt on the other hand. Therefore,
Deviating from the effective nozzle-like flow box structure, it is necessary in large and low cases to provide a "folded" flow path.

The invention is based on the problem of further improving the known apparatus in such a way that cellulose sheets with high quality, ie, uniform fiber distribution, can be produced even at very high wire running speeds.

This object is solved by the combination of features specified in patent claim 1. Thereby, the wire belt is no longer supported by the outer surface of one of the two flow guide walls of the flow box in order to introduce it into the sheet-forming zone.

Rather, for this purpose the support device arranged in the loop of the wire belt is provided with a convexly curved wire support surface. This has a two-fold effect: (a) in the region of the flow box outlet, there is sufficient space for a stable structure of the flow guide wall, so that the passage defined by this is substantially obtained without having to be curved. Preferably, the pulp flow can be guided without curvature, ie substantially straight. Thus, it is possible to eliminate the risk of cross currents occurring which would interfere with the uniformity of the fiber sheet formed.

(b) It is possible to feed the wire belt together with the cellulose sheet already formed thereon to the sheet forming zone of an additional flow box.
Thus - as is known in other multilayer paper machines (DE 2552485, FIG. 4) - a second fiber sheet layer can be formed directly on the already existing fiber sheet layer. in this case,
As is known, the fiber sheet layer already present serves as an auxiliary filter layer during the dewatering of the additional layer, so that only a small amount of fine fibers and filler is discharged with the backwater. Furthermore, the placement of the flow box is no longer restricted by felt. Thus, for example, an effective nozzle-like flow box can be used.

From FIG. 2 of German Publication No. 1931686 (=U.S. Pat. No. 3,582,467) it can be seen that the flow box has a convexly curved wire guide surface lying inside the wire loop in the area of the outlet of the flow box. It is known that it is equipped with a dehydration box. The dewatering box is swingable in the direction towards the outlet of the flow box or in the opposite direction.

It has a plurality of webs extending transversely to the direction of sheet travel, with dewatering slits between the webs. However, such dewatering boxes have the disadvantage of causing uneven fiber distribution of the paper sheet and high losses of fines and fillers, especially if they are arranged directly at the beginning of the sheet forming zone. are doing. Additionally, double wire paper machines have become a problem there.
This type of paper machine requires high costs due to the two wires. Furthermore, the much higher energy requirements for operation and the higher costs for cleaning the two wires have to be taken into account. In many double wire paper machines, sheet formation is further hindered by a long free pulp flow between the flow box outlet and the sheet forming zone. To avoid this drawback,
According to DE 1931686, a flexible flow guide wall must be provided which abuts the wire belt. In the embodiment according to the invention, this disadvantage is eliminated from the beginning in that the pulp jet is guided on at least one side by a continuous flow guide wall (sliding show).

On the other side of the pulp jet, the free section can be kept particularly short by constructing the wire support device arranged in the loop of the wire belt according to claim 2. This provides a simple solid wire support rail which has no dewatering slits and whose radius of curvature can therefore be selected to be particularly small. Compared to a rotating roller, this structure
This has the advantage that there is no need to consider the critical rotational speed. It can thus be designed completely independent of machine speed.

In order to be able to compensate for possible errors in the manufacture of the flow guide walls of the rail or of the adjacent flow box, the following is carried out in accordance with claim 3: The wire support rail is assembled as a whole in a manner known per se. It is not only movable transversely to the pulp flow (toward or against the outlet of the flow box). Rather preferably, it is ensured that the travel path of the rail is adjustable to different extents over the entire width of the machine.
For this purpose, for example, a plurality of individually adjustable screw shafts can be provided over the entire length of the rail.

Claim 4 is based on the knowledge that wire belts, upon introduction into the sheet-forming zone, may introduce air into the pulp stream which may interfere with the sheet-forming process. According to claim 4, this risk arises when the air present in the wire eye moves from the wire eye into the loop of the wire belt upon impact of the pulp jet behind the line leaving the wire support rail of the wire belt. This can be prevented by running away.

French Publication Specification No. 2457430 (= International Publication
From WO 80/02575) a wire section is known, in which a wire belt is guided into the sheet-forming zone via suction boxes which each have one wire support rail only at the inlet and outlet ends. This causes negative pressure in the suction box to cause strong bending of the wire belt. The pulp stream is covered in the sheet forming zone by a flexible lip that is fixed to the flow guide wall above the flow box. This lip curves to accommodate the bending of the wire belt. A disadvantage of this known construction is that - in addition to the high energy requirements for the generation of negative pressure - the flexible lip can vibrate. This generally results in strong fluctuations in the areal weight of the paper produced, and there is also a risk of breakage. Furthermore, the curvature of the sheet-forming zone can be controlled at most by changes in wire tension or vacuum. The invention, on the other hand, makes it possible for the stationary sliding shoe to be provided with a predetermined curved shape precisely and not only in the direction of travel of the wire belt, but also transversely thereto, for example at the edges.

The curved slide show may be configured as a fixed extension of the associated flow guide wall. Preferably, however, the slide show is configured to be adjustable transversely to the pulp flow (claim 5). Thereby, if necessary, the slide show can be pushed into the pulp passage a little, and the size of the outlet opening can thus be adjusted in order to change the outlet flow rate. Also in the case of a slide show, the travel stroke can be adjusted to different sizes over the entire width of the machine (claim 6). This makes the pulp flow uniform across the width of the machine. The measures indicated in claim 7 can contribute to stabilizing the pulp flow at the outlet.

Due to the decreasing curvature of the slide show in the direction of flow (claim 8), account can be taken of the fact that the dewatering at the beginning of the sheet-forming zone takes place more quickly than at the end. In this case, the wire belt therefore has a substantially uniform curvature in the dewatering zone. However, in order to achieve a pressure drop that compensates for the wear of the slide show in the direction of flow, especially when there are high demands regarding the uniformity of the sheet to be formed,
It is also suitable for the curvature of the slide show to be strongly reduced in the flow direction. The average radius of curvature of the slide show generally lies between 100 and 800 mm, preferably between 150 and 300 mm.

In order to precisely define the end of the dewatering zone, the wire belt should preferably be deflected slightly by at most 5° by the discharge end provided at the end of the slide show (claim 9). .

In order to further dewater the formed cellulose sheet, an overpressure chamber formed according to claim 10 can be provided. The pressure inside this overpressure chamber is generally
It should lie between 500 and 10,000 Pascals, preferably between 2,000 and 7,000 Pascals.

If multilayer cellulose sheets are to be produced, the features of claim 11 and/or 12 can advantageously be applied. In this case, a plurality of flow boxes, for example two flow boxes, are arranged in succession on the same wire belt so that at least one second fiber sheet layer is formed on the first fiber sheet layer. is the premise. As already mentioned above, the first fiber sheet layer then serves as a filter auxiliary layer during the dewatering of the second fiber sheet layer. A higher retention of fine fibers and fillers is thus achieved in this process. The problem of obtaining such high retention also during dewatering of the first fiber sheet layer forms the basis of another idea of the invention. The solution to this problem is claimed in claim 1.
4. For example, in the case of a wire section with two flow boxes, this is done as follows. Backwater exiting the first flow box, which has a relatively large amount of fines and filler, is used to dilute the pulp to the second flow box. Thereby, a paper sheet is reached in which the majority of the fine fibers and fillers "lost" after the first flow box are formed. In the case of known paper machines, on the other hand, the content of fine fibers and fillers in the backwater of the first flow box increases gradually (particularly when using certain types of waste paper as raw material). Therefore, the problem often arises that the desired paper quality can no longer be achieved. Furthermore, a larger amount of backwater (than would otherwise be necessary) has to be removed from the circuit, whereby the paper mill's filter system is subjected to a higher load.
All these disadvantages can be eliminated by the features of patent claim 14. This is best accomplished - in the above example with two flow boxes - when approximately equal amounts of backwater occur in both sheet forming zones. For this purpose, it must be ensured that any excess backwater can spill from one backwater system to the other.

Embodiments of the invention will be explained below based on the drawings.

The wire section shown in FIG. 1 has an endless wire belt 10 running through guide rollers 11 to 14. One of the guide rollers is an adjustment roller 13, and the other one is a tension roller 14. The whole flow box is code 15
It is shown by. In addition, as is well known, a dispersion tube 1
6. An outlet channel 20 with an outlet 21 defined by a tube row 17 and two flow guide walls 18 and 19 is attached.

The flow guide wall, designated by the reference numeral 19, has an extension in the form of a convexly curved sliding show extending beyond the outlet 21 in the direction of flow. The slide show 22, like the other parts of the flow box, extends over the entire width of the wire belt 10. This progresses beyond the slide show 22. In the region of the outlet 21 the wire belt 10 is guided via a fixed rail 23 with a convexly curved wire support surface 24 arranged inside the loop of the wire belt (see FIG. 2).

The pulp jet exiting the outlet 21 reaches a sheet forming zone 25 which is curved and tapered in correspondence with the slide show 22 . At this time, intense dehydration takes place inside the loops of the wire belt.

The rail 23 is fixed to the horizontal beam 26,
The transverse beams are placed at each end on one support 27 and are movable there transversely to the direction of flow into the sheet-forming zone 25, i.e. in the direction of the outlet 21 or vice versa. be. A reservoir for receiving backwater is indicated at 28. A suction box 29 may be provided to further dewater the formed paper sheet.

A reinforcing wall 30 of the flow box 15 that supports the slide show 22 forms a hollow portion 31 together with the flow guide wall 19. This has connecting pipe 32
Compressed air is supplied through the openings 33 and reaches an overpressure chamber 34 located behind the slide shoe 22 . This is limited to the outside world by a labyrinth formed by three rails 35. This rail 35 is connected to the reinforcing wall 30
The rail support member 36 is fixed to the rail support member 36 .

Felt belt 37 (or wire belt)
The paper sheet advances through the suction pick-up roll 38 and the formed paper sheet is transferred to the wire belt 1.
0 and guide to other dewatering or drying equipment not shown in the drawings.

In FIG. 2, some further construction details are shown: a fixed wire support rail 23, which can be manufactured, for example, from ceramic;
is fixed to the rail holding member 23b.
It is connected to the transverse beam 26 by a plurality of screws 41 (only one of which is shown in the drawing) distributed over the entire length of the rail. Furthermore, the transverse beam is equipped with threaded shafts 42 each having two nuts 43 distributed over its entire length. Each of the screw shafts 42 has a small hole 44 formed in the rail holding member 23b.
extends through. By rotating the nut 43 after loosening one of the screws 41, the rail holding member 23b having the rail 23 can be attached to the other screw shaft 42.
may locally be brought somewhat closer to the flow guide wall 18 than in the region of . In this way, possible manufacturing errors can be compensated for.

After leaving the outlet 21, the pulp jet is free only for a short section on the side facing the wire belt 10 (indicated by the dotted line 7 in FIG. 2). The pulp jet is
The wire belt 10, which is separated from the rail 23, collides with the wire belt 10 at a point indicated by 8, which is previously indicated by 9.

In general, the length of the free pulp jet, i.e. the outlet 2
The distance between the rail 23 and the end of the flow guide wall 18 is adjusted to be as small as possible so that the distance from 1 until the pulp jet impinges on the wire belt 10 is as small as possible. The radius of curvature k of the rail 23 is smaller than 100 mm in both cases, which also contributes to shortening the free pulp jet.

The slide show 22 is fixed to a plurality of adjustment rods 45 distributed over its entire length. Only one of these rods 45 appears in the drawing. The rod is located in a bore 46 in the reinforcing wall 30 and is movable therein in the axial direction, ie in the direction of the outlet 21 or vice versa. Each adjustment rod 45 rotatably supports an adjustment nut 47 whose external thread is engaged with a threaded hole in the sealing rail support member 36. The adjusting nuts 47 are individually rotatable. Thus, the travel stroke of the slide show 22 can be adjusted to different sizes over the width of the machine.

The movable sliding shoe 22 abuts the end of the flow guide wall 19 with a sealing surface 48 . This lies before the end of the flow guide wall 18, ie before the outlet 21, seen in the flow direction. Therefore, by adjusting the slide show 22, the inner width of the outlet 21 and the flow rate of the outlet can be changed.

The curved surface of the slide show 22 that is contacted by the pulp stream can advantageously be formed as follows. In the region of the outlet 21, the curved surface is flat or slightly curved with a very large radius of curvature K. Following this there is a region with a relatively strong curvature (radius of curvature r) and finally again a region with a weak curvature (radius of curvature R).

In FIG. 2, a sharp discharge edge on the sliding shoe 22 is indicated at 50, and a tangent thereto located on a curved surface is indicated at t. The wire belt 10 is preferably guided so as to allow for an angle of about 0.5 DEG to 5 DEG with the tangent t, measured when the machine on which the wire belt 10 is stretched is at rest.

In FIG. 1, the flow box 15 is the outlet 2.
It is arranged vertically with 1 facing down. However, any other arrangement is possible instead. FIG. 3 shows a wire section with two flow boxes. The first flow box 15a is arranged horizontally, and the second flow box 15a
b is arranged vertically as in FIG. The two flow boxes 15a and 15b are
They are distinguished by different slide shows 22a and 22b. In the first flow box 15a, the curved surface of the slide shoe 22a is relatively short and slightly curved. Correspondingly, the pulp stream is deflected by approximately 45° in the sheet forming zone. In contrast, the slide show 22b of the second flow box 15b
has a longer curved surface that is more strongly curved. With this treatment, the first flow box 15
The higher dewatering resistance caused by the fibrous sheet layer formed in a is compensated. In the first flow box 15a, it is desirable to achieve as low a dewatering rate as possible due to a relatively large average radius of curvature during sheeting of the first fibrous layer. Thus, the fiber sheet at the end of the wire section can be more easily removed from the wire belt, since the fibers are washed less strongly and do not get into the wire eyes. Furthermore, very few fine fibers and fillers are washed through the wire belt.

In FIG. 3, each flow box 15a, 15
Separate backup water reservoirs 28a and 2
8b is associated. Backwater pipes 51a and 51b lead from each of these reservoirs to backwater containers 52a and 52b.
As already mentioned above, in the next step the backwaters of the two flow boxes are exchanged with each other. That is, the circulation pump 53a delivers the fluid to the first flow box 15a (via the pipe 54a).
is connected on its suction side to the backwater container 52b, whereas the other circulation pump 53b (with pressure pipe 54b) is connected to the backwater container 52a. There is a connection at 55 between the two backwater containers. Thus, a portion of the backup water that has entered container 52a that is not needed by pump 53b may overflow into container 52b.

FIG. 4 shows a wire section for producing a three-layer cellulose sheet. The three flow boxes 15', 15'' and 15 are again identical to each other, except for the slide shoes 22', 22'', 22 which are formed differently. The sealing rail support member 36 on the flow box with the sealing rail 35 (see FIGS. 1 and 2) is shown in FIG.
(as in the figure) not shown. It is clear that the closed rail support must be adapted to the different inclinations of the wire belt. Fixed wire guide rails 23'' and 2 associated with flow boxes 15'' and 15
3 are fixed to the discharge ends of the suction boxes 29' and 29'' rather than to the individual transverse beams.
Manufacturing costs are thus reduced.

In FIGS. 3 and 4, the individual flow boxes are arranged so that they can be easily lifted off the wire belt and, if necessary, operated without the wire belt contacting its slide show, for example with the exception of one flow box. can be made swingable.

In all embodiments, the paper sheet is removed from the wire belt - instead of by suction roll 38 (FIG. 1) - by rail or leveling rollers ("lick-up" or suction box). , and finally by a blow box.The drive of the wire belt takes place via one or more of the wire guide rollers 11 to 14 (FIG. 1).The tension of the wire is between 3 and 10 kN/m. should be within the general range of

According to another idea of the invention, claim 1
14 can be combined with one of the known sheet forming units, such as a conventional fourdrinier or suction breast roll or double wire former. In this case, one (or more) flow boxes 15 in FIG.
can preferably be arranged together with the components 23 and 26 to 29 upstream of the known sheet-forming unit in the direction of wire travel. In the case of a double wire former, as shown in FIG. 1, the flow box 15, which has a flow direction from the bottom to the top, is a wire that approaches the double wire zone in a direction from the bottom to the top before the double wire zone. The arrangement is such that it is in contact with the belt.

[Brief explanation of drawings]

Figure 1 is a schematic sectional view of a wire section with one flow box, Figure 2 is a partially enlarged sectional view of Figure 1, and Figure 3 is a wire section with two flow boxes and associated backwater circulation. FIG. 4 is a schematic cross-sectional view of a wire section having three flow boxes. 10...Wire belt, 11 to 14...Guide roller, 15, 15a, 15b, 15', 1
5'', 15... Flow box, 16... Dispersion tube, 17... Tube bundle, 18, 19... Flow guide wall, 20... Outlet path, 21... Outlet, 22, 2
2a, 22b, 22', 22'', 22... Slide show, 23, 23'', 23, 35... Rail, 24... Wire support surface, 25... Sheet forming zone, 26... Horizontal beam, 27 ...support stand,
28, 28a, 28b...reservoir, 29, 29',
29″...Suction box, 30...Reinforcement wall,
31... Hollow part, 32... Connection pipe, 33... Opening, 34... Overpressure chamber, 36... Rail support member,
37...Felt belt, 38...Suction pick-up roll, 41...Screw, 42...Screw shaft, 43...Nut, 44...Small hole, 45...Adjustment rod, 46...Bore, 47...Adjustment Natsuto,
48... Sealing surface, 50... Discharge edge, 51a, 5
1b... Backwater pipe, 52a, 52b...
...Backwater container, 53a, 53b...Circulation pump, 54a, 54b...Pipe, 55...Connection part.

Claims (1)

Claims: 1. The following features: (a) The flow box 15 has, seen in longitudinal section, a passage 20 defined by two flow guide walls 18, 19 and provided with an outlet 21; (b) one of the two flow guide walls 19 extends beyond the outlet 21 and is convex; (c) the pulp flow is confined in the region of the sheet forming zone 25 by the slide show 22 on one side and by the wire belt 10 on the other side; (d) a wire support device 23 having a convexly curved wire support surface 24 is provided for introducing the wire belt into the sheet forming zone 25; (e) the extension 22 of the flow guide wall 19 extends substantially without change in direction in the region between the end of the other flow guide wall 18 and the start end 8 of the sheet forming zone 25; ) The support device 23 is an endless wire belt 1
A wire section of a paper machine, characterized in that the wire section is disposed inside a zero loop. 2 The wire support device 23, via which the wire belt 10 is fed to the dewatering zone 25, is a fixed and robust rail, the wire support surface 2
4. The wire part according to claim 1, characterized in that the radius of curvature k of 4 is smaller than 200 mm. 3. The wire support rail 23 is arranged so that the separation line 9 of the wire belt 10 from the rail 23 is located in front of the collision line 8 of the pulp flow against the wire belt 10 in the wire traveling direction. , the wire portion according to claim 2. 4. The wire section according to any one of claims 1 to 3, wherein the slide show 22 is adjustable laterally with respect to the pulp flow. 5 The sealing surface 48 is connected to the outlet 21 with respect to the direction of flow.
5. The wire portion according to claim 4, wherein the wire portion is disposed in front of the wire portion. 6. Claim 1, characterized in that the radius of curvature r, R of the slide show 22 in the region of the sheet forming zone 25 increases in the flow direction.
6. The wire portion according to any one of 5 to 5. 7. According to any one of claims 1 to 6, the slide shoe has a discharge edge, characterized in that the wire belt 10 undergoes a slight change of direction (angle a) by the discharge edge 50. wire part. 8 Behind the slide show 22, seen in the direction of flow, is an overpressure chamber 34 of the same width as the machine to be supplied with air.
, characterized in that the overpressure chamber is sealed off by one or more restricting slots (rails 35) without contacting the cellulose sheet formed on the wire belt, A wire portion according to any one of claims 1 to 7. 9. At least one additional flow box on the wire belt, characterized in that the length of the arc measured in the flow direction of the slide shows 22a, 22b increases in the direction of travel from the flow box 15a to the flow box 15b. attached,
A wire portion according to any one of claims 1 to 8. 10. At least one additional flow box is attached to the wire belt, characterized in that the average radius of curvature of the slide shows 22a, 22b decreases from flow box 15a to flow box 15b. 10. The wire portion according to any one of 1 to 9. 11 One additional flow box 15″, 15
Fixed rails 23″, 23 attached to the wire belt and located inside the loop of the wire belt
11. A wire portion according to claim 9, characterized in that the suction box 29', 29'' is disposed at the discharge end of the suction box 29', 29''.